This is a diamondback rattlesnake (Crotalus atrox). Yes, I was too close. Snake chaps are a wonderful thing. I do not recommend needing them, however.
This fellow was sunning on my porch, trying to warm up after the cold winter. You know you are a photographer when you run for the camera, not the hoe, upon seeing a snake. He is a Texas Rat Snake (Elaphe obsoleta lindheimeri), and eats mice and other vermin, so I do not mind him living under the house.